EP2757352B1 - Control system and management method of a sensor - Google Patents

Description

The present invention relates to a measuring circuit comprising a control block for controlling said circuit, a time base for providing a clock signal for clocking said circuit, a sensor block arranged to provide an output signal, said measuring circuit comprising in in addition to a first counter block clocked at the clock frequency and a second counter block clocked by the frequency of the output signal of the sensor block.

BACKGROUND TECHNOLOGY

The humidity sensors consist of two armatures each provided with a plurality of arms. The two armatures are arranged to be nested one inside the other and have a dielectric between them. These armatures are supplied with voltage so that their nesting leads to the creation of a capacitance.

This moisture sensor works so that when the moisture content in the air increases, water molecules seep between the two plates in the dielectric. This water infiltration causes a modification of the capacity which makes it possible to quantify the humidity rate during a measurement by applying a tension. The humidity sensor may be a structure connected to an integrated circuit or be directly included in the integrated circuit.

To determine a humidity value from this capacity, several methods are known.

A first method consists in connecting the output of the humidity sensor, a charge amplifier to obtain a voltage signal representative of the humidity level. This signal is sent in a signal conditioner preparing the signal to be sent into an analog digital converter so as to provide a numerical value N. This numerical value N is then sent in a circuit which linearizes it because the curve of the capacitance in function humidity is not linear. This gives a numerical value N which is a function of the capacitance C of the sensor.

A second method consists in connecting the output of the humidity sensor, a circuit for obtaining a frequency signal representative of the humidity level. Indeed, this variable capacitance is inserted into a resonator so as to make an RC oscillator. Consequently, the output frequency of said resonator is dependent on the value of the capacitance and therefore of the humidity level. This frequency is sent into a signal conditioner preparing the signal to be sent into an analog digital converter so as to provide a digital number N. This signal conditioner may be a digital frequency demodulator or a set of a circuit for converting this frequency signal into voltage and converting it to a digital value N which will be processed to obtain the value of the physical quantity.

A disadvantage of these two methods is that they require a circuit which comprises a large number of components, that is to say a circuit whose manufacturing cost is high but also which requires a larger silicon surface when the integration into an integrated circuit. As a result, the number of measuring circuits per board is smaller.

The document JP S58 182502 A describes a measuring circuit according to the state of the art.

SUMMARY OF THE INVENTION

The object of the invention is to overcome the drawbacks of the prior art by proposing to provide a measurement circuit that is accurate for all the components used and that is inexpensive, particularly when implemented in an integrated circuit.

For this purpose, the invention relates to a measuring circuit comprising a control block for controlling said circuit, a time base for providing a clock signal for clocking said circuit, a sensor block arranged to provide an output signal, said circuit measuring device further comprising a first counter clocked at the clock frequency and a second counter clock clocked by the frequency of the output signal of the sensor unit, characterized in that the sensor unit is arranged to provide an output signal, a first signal whose frequency is representative of the measured physical quantity or a second signal whose frequency is a reference frequency and in that the control block controls the measuring circuit so that the first and second counter blocks operate according to a first phase in which the first and second counter blocks count and a second phase in which the first counter block counts and the second counting counter block and in that the clocking frequency of the second counter block in the first phase is different from that in the second phase.

In a first advantageous embodiment, the second counter block is clocked by the frequency of the second signal during the first phase and by the frequency of the first signal during the second phase.

In a second advantageous embodiment, the control block comprises a control circuit and a sequencer block.

In a third advantageous embodiment, the second counter block comprises a zero detector connected to the sequencer block.

In another advantageous embodiment, the sensor block comprises an oscillator, a first variable-value electronic component and a second fixed-value electronic component, the first and second electronic components being connected in parallel to the oscillator via switching means and in that the first electronic component provides the first signal and in that the second electronic component provides the second signal.

In another advantageous embodiment, the first component and the second component each comprise a first terminal and a second terminal and in that the switching means comprise a first and a second controllable switch connected in series between the first terminal of the first component. and the first terminal of the second component and a third and a fourth controllable switch connected in series between the second terminal of the first component and the second terminal of the second component, the connection point between the first and second controllable switch and the connection point. between the third and fourth controllable switches being connected to the oscillator unit.

In another advantageous embodiment, the first component and the second component are capacitors.

In another advantageous embodiment, the first component and the second component are resistors.

In another advantageous embodiment, the first component and the second component are inductance coils.

In another advantageous embodiment, the sensor unit is able to measure the humidity level.

In another advantageous embodiment, it further comprises a linearization circuit.

1. 1) sélectionner le second signal dont la fréquence est une fréquence de référence comme signal de sortie du bloc capteur
2. 2) démarrer le comptage du premier bloc compteur cadencé par le signal d'horloge et du second bloc compteur cadencé par le signal de sortie du bloc capteur ;
3. 3) lorsque le premier bloc compteur atteint un premier nombre prédéfini, il se remet à zéro et le second bloc compteur s'arrête de compter
4. 4) sélectionner le premier signal dont la fréquence est représentative de la grandeur physique mesurée comme signal de sortie du bloc capteur ;
5. 5) démarrer le comptage du premier bloc compteur cadencé par le signal d'horloge et le décomptage du second bloc compteur à partir de la valeur comptée lors l'étape 3), ledit second bloc compteur étant cadencé par le signal de sortie du bloc capteur ;
6. 6) lorsque le second bloc compteur atteint un second nombre prédéfini :
   • arrêter le comptage du premier bloc compteur et le décomptage du second bloc compteur et
   • sauvegarder la valeur comptée par le premier bloc compteur ;
7. 7) déterminer, à partir de la valeur comptée par le premier bloc compteur, la valeur de la grandeur physique mesurée par le bloc capteur.

The invention also relates to a method for managing a measuring circuit comprising a control block for controlling said circuit, a resonator for supplying a clock signal for clocking said circuit, a sensor block arranged to provide an output signal, said measuring circuit further comprising a first counter clocked at the clock frequency and a second counter clock clocked by the frequency of the output signal of the sensor unit, characterized in that the sensor unit is arranged to supply as an output signal, a first signal whose frequency is representative of the measured physical quantity or a second signal whose frequency is a reference frequency and that said method comprises the following steps:

1. 1) select the second signal whose frequency is a reference frequency as the output signal of the sensor block
2. 2) starting the counting of the first counter block clocked by the clock signal and the second counter block clocked by the output signal of the sensor unit;
3. 3) When the first counter block reaches a first predefined number, it resets to zero and the second counter block stops counting
4. 4) selecting the first signal whose frequency is representative of the physical quantity measured as the output signal of the sensor unit;
5. 5) starting the counting of the first counter block clocked by the clock signal and the counting down of the second counter block from the value counted in step 3), said second counter block being clocked by the output signal of the sensor block ;
6. 6) when the second counter block reaches a second predefined number:
   • stop the counting of the first counter block and the countdown of the second counter block and
   • save the value counted by the first counter block;
7. 7) determining, from the value counted by the first counter block, the value of the physical quantity measured by the sensor block.

In another advantageous embodiment, the second predefined number is zero.

In another advantageous embodiment, the first predefined number is dependent on the resolution of the counter.

In another advantageous embodiment, it further comprises a final step for linearizing the value counted by the first counter block as a function of the measured physical quantity, this step of squaring said value counted by the first counter block.

The invention further relates to an electronic portable object comprising the measuring circuit according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

• les figures 1 et 2 représentent de manière schématique exemple de circuit de mesure selon la présente invention ;
• la figure 3 représente un diagramme de fonctionnement du procédé selon l'invention ; et
• la figure 4 représente de façon schématique l'unité oscillateur selon l'invention.

The aims, advantages and characteristics of the measuring circuit according to the present invention will appear more clearly in the following detailed description of at least one embodiment of the invention given solely by way of nonlimiting example and illustrated by the accompanying drawings on which :

• the Figures 1 and 2 show schematically an example measuring circuit according to the present invention;
• the figure 3 represents an operating diagram of the method according to the invention; and
• the figure 4 schematically represents the oscillator unit according to the invention.

DETAILED DESCRIPTION

The Figures 1 and 2 represent the measuring circuit 100 according to the invention. This measuring circuit 100 can be integrated in a portable object such as a watch or a telephone or communication device or a portable measuring device. This measuring circuit 100 comprises a control block 102 comprising a control circuit 103 used to control the measuring circuit 100. The measuring circuit 100 is clocked by a time base 104 which may be for example an RC oscillator or an oscillator quartz and which provides a signal Fclk.

This measuring circuit 100 further comprises a sensor block 106 to provide an indication of a physical quantity. In this case, the sensor block 106 is used to measure the humidity level. The sensor unit 106 comprises a humidity sensor or humidity measurement unit 109. This humidity sensor 109 is in the form of a micro-mechanism of the MEMS type composed of two electrically powered plates. As moisture increases, water molecules seep between the plates so that the capacity between them varies. The humidity sensor 109 will be represented by a variable capacitor Cs comprising a first contact terminal and a second contact terminal.

avec gm qui est la transconductance des transistors MOS N3 et N4 et C_L une capacité de charge interne.Advantageously according to the invention, the sensor unit 106 further comprises the sensor 109, an oscillator unit 107 comprising a reference capacitor C ₀ and an oscillator RC 107a. The reference capacitor C ₀ comprises a first contact terminal and a second contact terminal. The first contact terminal of the capacitor C ₀ is connected to the first contact terminal of the humidity sensor via switching means 120 such as a first T1 and a second controllable T2 switch. The second contact terminal of the capacitor C ₀ is connected to the second contact terminal of the humidity sensor via switching means such as a third T3 and a fourth T4 controllable switch. The controllable switches may be transistors. This configuration makes it possible to connect the reference capacitor C ₀ or the variable capacitor C _s acting as a humidity sensor to the oscillator RC 107a. This RC oscillator 107a operates on the principle of an RC circuit oscillating, the frequency being dependent on the value of the resistor R and the capacitance value of the capacitor C so that the frequency of an RC oscillator is: $f=\frac{1}{4\pi }\sqrt{\frac{\mathrm{boy\; Wut}m}{R\mathrm{.}\mathrm{VS}s*\mathrm{VS}\mathrm{The}}}$

with gm which is the transconductance of MOS transistors N3 and N4 and C _L an internal charge capacity.

In the case of the present invention, the oscillator unit RC 107 comprises three elements, that is to say a relaxation oscillator 1070 connected to a polarization block 1072 and to a clock extractor block 1071 as visible in FIG. figure 4 . The relaxation oscillator comprises two pairs of transistors, a first pair of transistors N1 and N2 each having their source connected to the ground of the circuit and the drain connected to the source of a transistor. The drain of the transistor N1 is connected to the source of the transistor N3 and the drain of the transistor N2 is connected to the source of the transistor N4. The drains of transistors N3 and N4 are each connected to a terminal of a resistor having its other terminal connected to a supply voltage via the extractor module. The gates of the transistors N1 and N2 are connected to the polarization block while the gate of the transistor N3 is connected to the drain of the transistor N4, the gate of the transistor N4 being connected to the drain of the transistor N3.

The relaxation oscillator also comprises four switching transistors (T1, T2, T3 and T4) which are the switching means 120. The transistors T1 and T3 are arranged so that the drain of T1 is connected to the drain of N1 and that the source of T3 is connected to the drain of N2, the capacitor C ₀ being connected between the source of T1 and the drain of T3. Transistors T2 and T4 are connected so that the source of T2 is connected to the drain of N1 and the source of T4 is connected to the drain of N2. The gates of T1 and T3 are connected to a first terminal IN1 and the gates of T2 and T4 are connected to a second terminal IN2 so that they can be switched. The structure of the sensor, ie the variable capacitance Cs is connected between the drains of T2 and T4. It is found that the relaxation oscillator has an internal capacitance C _L between the terminal of the resistor R1 connected to the transistor N3 and the terminal of the resistor R2 connected to the transistor N4. We obtain a frequency: $f=\frac{1}{4\pi }\sqrt{\frac{\mathrm{boy\; Wut}m}{R\mathrm{.}\mathrm{VS}s*\mathrm{VS}\mathrm{The}}}$

As a result, the frequency supplied at the output of the sensor unit 106 will be dependent on the capacitance of the variable capacitor C _s to give a first frequency signal F _s representative of the measured physical quantity or of the reference capacitor C ₀ to give a second signal of frequency F _ref which is a reference signal.

In addition, the measuring circuit 100 includes a first counter block 108 connected to the time base 104 and a second counter block 110 connected to the output of the sensor block 106. The first counter block 108 and the second counter block 110 are synchronous with each other. that is, they are controlled simultaneously. To control the first 108 and the second counter block 110, the control circuit 103 is used. The control block 102 includes a counter synchronization unit. The control block 102 further comprises a sequencer block 112. This sequencer block 112 is used to act on both the first 108 and second 110 counter blocks but also on the sensor block 106. This configuration makes it possible to use a method of calculating the physical quantity according to the invention. This method is called a double ramp method. This method takes place in two phases, a diagram of which is visible at figure 3 .

In a first phase, the control circuit 103 and the sequencer block 112 control the measuring circuit 100. The sequencer block 112 controls the sensor block so that the output frequency of the block sensor 106 is the reference frequency F _ref that is to say that the sequencer block 112 makes the second T2 and fourth T4 switches are open while the first T1 and third T3 switches are closed.

In addition, the control circuit 103 and the sequencer block 112 control the measuring circuit 100 so that the first counter block 108 and the second counter block 110 start counting. The first counter block 108 counts by being clocked by the frequency of the time base F _clk while the second counter block 110 counts by being clocked by the output frequency of the sensor block is the reference frequency F _ref . The first counter block 108 is configured to count to a first predefined number N _clk . The second counter block 110 is synchronous with the first counter block, ie the first counter block 108 and the second counter block 110 begin to count or start simultaneously. When the first counter reaches the predefined number N _clk , it stops counting and the second counter block 110 also stops counting.

Once the first counter block 108 has arrived at the predefined number N _clk and it goes to zero, the second phase can begin. This zero crossing is detected by the control circuit 103. This control circuit 103 and the sequencer block 112 act on the second counter block 110 so that it switches from a counting mode to a countdown mode.

This phase consists firstly in switching the output frequency of the sensor block 106. The sequencer block 112 acts so that the second T2 and fourth T4 switches are closed while the first T1 and third T3 switches are open.

The output frequency is then dependent on the physical quantity measured by the sensor.

Then, in this second phase, the first counter block 108 starts counting again while the second counter block 110 begins counting down. The second counter block 110 starts to count down from the number N _ref saved. The counting is then done by being clocked by the output frequency of the sensor block 106 that is to say the frequency representative of the measured physical quantity F _s . Each counter block is provided with a zero detector so that when the second counter block 110 reaches a second predefined number that is zero, the first counter 108 also stops counting. The number N _s counted by said first counter 108 is then saved.

De ce fait : $$N_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{Fclk}}=N_{\mathit{ref}}$$

Ensuite, de la seconde phase, on admet que $$N_s\times \frac{1}{\mathit{Fclk}}=N_{\mathit{ref}}\times \frac{1}{\mathit{Fs}}$$

En combinant les équations 1 et 2, on obtient alors : $$N_s=N_{\mathit{ref}}\times \frac{\mathit{Fclk}}{\mathit{Fs}}=N_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{Fclk}}\times \frac{\mathit{Fclk}}{\mathit{Fs}}=N_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{Fs}}$$

En connaissant les formules des fréquences des oscillateurs RC pour les fréquences F_ref et F_s, on peut introduire ces formules dans l'équations 4 ce qui donne : $N_s=N_{clk}\times \sqrt{\frac{Cs}{C0}}$

The different values of N _ref , N _clk and the values of the different frequencies make it possible to calculate the value of the physical quantity. These values are transmitted to the control circuit 103 or to a calculation circuit not shown in the figures, which is responsible for supplying the value of the measured physical quantity.
Indeed, from the first phase, we admit that $${\mathrm{NOT}}_{\mathit{clk}}\times \frac{1}{\mathit{Fclk}}={\mathrm{NOT}}_{\mathit{ref}}\times \frac{1}{\mathit{Fref}}$$

Thereby : $${\mathrm{NOT}}_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{Fclk}}={\mathrm{NOT}}_{\mathit{ref}}$$

Then, from the second phase, we admit that $${\mathrm{NOT}}_s\times \frac{1}{\mathit{Fclk}}={\mathrm{NOT}}_{\mathit{ref}}\times \frac{1}{\mathit{fs}}$$

By combining equations 1 and 2, we obtain: $${\mathrm{NOT}}_s={\mathrm{NOT}}_{\mathit{ref}}\times \frac{\mathit{Fclk}}{\mathit{fs}}={\mathrm{NOT}}_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{Fclk}}\times \frac{\mathit{Fclk}}{\mathit{fs}}={\mathrm{NOT}}_{\mathit{clk}}\times \frac{\mathit{Fref}}{\mathit{fs}}$$

By knowing the formulas of the frequencies of the oscillators RC for the frequencies F _ref and F _s , one can introduce these formulas in the equations 4 which gives: ${\mathrm{NOT}}_s={\mathrm{NOT}}_{\mathrm{vs}lk}\times \sqrt{\frac{\mathrm{VS}s}{\mathrm{VS}0}}$

We obtain a number N _s which is independent of the frequency of the time base. This has the advantage of having a circuit whose frequency of the time base 104 does not need to be precise because it does not affect the measured value.

Ce circuit de linéarisation 114 fournit en sortie S_NOUT. le nombre N_sl prêt à être utilisé par un processeur par exemple.To linearize the relationship between the capacitance measured by the sensor and the number N _s given by the counter 108, the number N _s is squared by a linearization circuit 114 to obtain the number N _sl which gives: ${\mathrm{NOT}}_{sl}={\mathrm{NOT}}_s^2={\mathrm{NOT}}_{\mathrm{vs}l\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="imgf0001.png"\; state="\{\{state\}\}">k</figure-callout>}}^2\times \frac{\mathrm{VS}s}{\mathrm{VS}0}\mathrm{.}$

This linearization circuit 114 outputs S _NOUT . the number N _sl ready to be used by a processor for example.

However, the number N _clk is dependent on the resolution of the circuit. Indeed, the data provided by the counter blocks 108, 110 are transmitted over a given number of bits, given that the higher the number of bits, the greater the accuracy. This means that the number N _clk is equal to 2 ^resolution with the resolution which is equal to the number of bits used.

Therefore, $${\mathrm{NOT}}_{\mathit{sl}}={\mathrm{NOT}}_{\mathit{clk}}^2\times \frac{\mathit{cs}}{\mathrm{VS}0}=2^{2\times \mathit{resolution}}\times \frac{\mathit{cs}}{\mathrm{VS}0}$$

It can therefore be seen that the number N _sl making it possible to obtain the value of the measured physical quantity is independent of the frequency of the measuring circuit 100 but also independent of the resistance R of the oscillator RC 107a of the sensor block 106 or of the transconductance g _m transistors of the oscillator 107a and the internal capacitance C _L of the oscillator 107a.

However, by a preliminary step during the manufacture of the sensor block 106, a calibration is performed so that the capacitance C _s for a moisture content of 0% is defined and that the capacitance C _s for a humidity level of 100% is defined. Therefore, it is defined that the number N _clk squared corresponds to the maximum moisture content and by a quick calculation, the moisture content can be determined as a function of the number N _sl measured.

It is conceivable that this method is used piecemeal. By this is meant that the first and second phases can be performed at regular intervals so as to have a measure of the physical magnitude at regular intervals. This measurement frequency can be set or parameterized. Similarly, it is possible that this measurement of the physical quantity using the method and the circuit according to the invention is made on demand. We understand that the user activates a command when he wants to know the value of the physical quantity.

In a variant, the measurement circuit 100 will not be limited to a sensor unit 106 for measuring the humidity level and will be extended to other measurable physical quantities with a capacitive sensor.

In an alternative, the sensor block 106 will not be capacitive but inductive. As a result, the sensor will comprise a variable inductance structure which will be connected to an oscillator of the LC type for example. Similarly, a sensor using a variable resistor could be used, said variable resistor being connected to an RC oscillator.

Claims (16)

1. Measuring circuit (100) comprising a control block (102) for controlling said circuit, a time base (104) for providing a clock signal (f_clk) in order to time said circuit, a sensor block (106) which is designed to provide an output signal, said measuring circuit comprising in addition a first counting block (108) which is timed to the clock frequency and a second counting block (110) which is timed by the frequency of the output signal of the sensor block, characterised in that the sensor block is designed to provide, as output signal, a first signal, the frequency of which is representative of the measured physical quantity (F_s) or a second signal, the frequency of which is a reference frequency (F_ref) and in that the control block controls the measuring circuit so that the first and second counting blocks function according to a first phase in which the first and second counting blocks count and a second phase in which the first counting block counts and the second counting block counts down and in that the timing frequency of the second counting block during the first phase is different from that during the second phase.
2. Measuring circuit according to claim 1, characterised in that the second counting block (110) is timed by the frequency (F_ref) of the second signal during the first phase and by the frequency (F_s) of the first signal during the second phase.
3. Measuring circuit according to claims 1 or 2, characterised in that the control block (102) comprises a control circuit (103) and a sequencer block (112).
4. Measuring circuit according to claim 3, characterised in that the second counting block (110) comprises a zero detector connected to the sequencer block (112).
5. Measuring circuit according to one of the preceding claims, characterised in that the sensor block (106) comprises an oscillator (107a), a first variable-value electronic component (C_s) and a second fixed-value electronic component (C₀), the first and the second electronic component being connected in parallel to the oscillator (107a) by means of commutation means (120) and in that the first electronic component makes it possible to provide the first signal and in that the second electronic component makes it possible to provide the second signal.
6. Measuring circuit according to claim 5, characterised in that the first component (C_s) and the second component (C₀) each comprise a first terminal and a second terminal and in that the commutation means comprise a first (T1) and a second (T2) controllable switch, which are connected in series between the first terminal of the first component and the first terminal of the second component, and a third (T3) and a fourth (T4) controllable switch which are connected in series between the second terminal of the first component and the second terminal of the second component, the connection point between the first and the second controllable switch and the connection point between the third and the fourth controllable switch being connected to the oscillator unit.
7. Measuring circuit according to claims 5 or 6, characterised in that the first component and the second component are capacitors.
8. Measuring circuit according to claims 5 or 6, characterised in that the first component and the second component are resistors.
9. Measuring circuit according to claims 5 or 6, characterised in that the first component and the second component are inductance coils.
10. Measuring circuit according to one of the preceding claims, characterised in that the sensor block (106) is able to measure the degree of moisture.
11. Measuring circuit according to one of the preceding claims, characterised in that it comprises in addition a linearization circuit (114).
12. Method for management of a measuring circuit (100) comprising a control block (102) for controlling said circuit, a time base (104) for providing a clock signal in order to time said circuit, a sensor block (106) which is designed to provide an output signal, said measuring circuit comprising in addition a first counting block (108) which is timed to the clock frequency and a second counting block (110) which is timed by the frequency of the output signal of the sensor block, characterised in that the sensor block is designed to provide, as output signal, a first signal, the frequency (F_s) of which is representative of the measured physical quantity or a second signal, the frequency (F_ref) of which is a reference frequency and in that said method comprises the following steps:

    1) selecting the second signal, the frequency of which is a reference frequency as output signal of the sensor block;

    2) starting the counting of the first counting block which is timed by the clock signal and of the second counting block which is timed by the output signal of the sensor block;

    3) when the first counting block reaches a first predefined number (N_clk), it is reset at zero and the second counting block stops counting;

    4) selecting the first signal, the frequency of which is representative of the measured physical quantity as output signal of the sensor block;

    5) starting the counting of the first counting block which is timed by the clock signal and the counting down of the second counting block from the value (N_ref) counted during step 3), said second counting block being timed by the output signal of the sensor block;

    6) when the second counting block reaches a second predefined number:

    - stopping the counting of the first counting block and the counting down of the second counting block and

    - saving the value (N_s) counted by the first counting block;

    7) determining, from the value (N_s) counted by the first counting block, the value of the physical quantity measured by the sensor block.
13. Method for management according to claim 12, characterised in that the second predefined number (N_s) is zero.
14. Method for management according to claim 12, characterised in that the first predefined number (N_clk) is dependent upon the resolution of the counter.
15. Method for management according to claim 12, characterised in that it comprises in addition a final step which is intended to linearize the value counted by the first counting block as a function of the measured physical quantity, this step consisting of squaring said value counted by the first counting block.
16. Wearable/portable electronic object, characterised in that it comprises the measuring circuit (100) according to one of the claims 1 to 11.

Images